Have been constipated lately and my recent bowel movement had little bits of pink in it like raw meat. its only happened once. can it be from straining or constipation? should i be worried?

Red bits in stool: If the red bits were bright red they could be from hard stool irritating the rectal vault, internal hemorrhoid or anus. At your age I wouldn't worry about a malignancy. Inflammatory bowel disease like ulcerative colitis has associated diarrhea usually. Drink plenty of water, eat soluble fiber or take a fiber supplement like Metamucil, exercise regularly take a stool softener daily. See MD as neede